The present invention relates to a rotating member supporting apparatus, and more specifically to a supporting apparatus for supporting a rotating member used in a corrosive environment, e.g., a melting furnace for alloy casting, molten-metal plating bath, or electroplating bath.
A conventional melting furnace used in a casting process for aluminum-based alloy or the like, for example, is found on page 11 of the April 1980 issue of the "Kinzoku" (Japanese trade magazine from Agune Co., Ltd.). According to this melting furnace, a fixed shaft extends from the outside of the furnace into a molten alloy in the furnace, and a rotating cylinder with blades at one end thereof is mounted on the fixed shaft with the aid of a bearing. The blades serve to stir the molten alloy for homogenization.
In the melting furnace of this type, however, the rotating blades are placed in the molten alloy, so that the bearing is located in the molten metal if it is disposed between the rotating cylinder and the fixed shaft. Thus, the bearing is left in a corrosive environment, resulting in early-stage decay. Conventionally, therefore, the other end portion of the rotating cylinder extends upward to be located above the surface level of the molten alloy, and the bearing rotatably supports the extended end portion of the rotating cylinder on the fixed shaft. As a result, the distance between those portions of the rotating cylinder corresponding to the bearing and the blades is extended, and the rotating cylinder is shaped like a cantilever supported by the bearing. With this arrangement, the blades whirl while they are rotating, so that stirring efficiency is too low for the molten alloy to be easily homogenized.
For the electroplating bath, a vertical plating bath is generally known which is stated in the "Comprehensive Bibliography of Iron-Making Machines & Equipment, 1977" (issued on Nov. 25, 1976, by Jukogyo Shinbun Publishing Co.). According to this plating bath, a steel plate is guided by a conductor roller and a hold-down roller outside the electroplating bath and a sink roller disposed in an electrolyte in the plating bath. Thus, the surface of the steel plate is plated when the steel plate is energized by a current flowing between an anode bar in the electrolyte and the conductor roller as a cathode. Both end portions of a supporting shaft of the sink roller are fitted in bores in a supporting member at the top end portion of the plating bath. Since the sink roller is rotated at high speed, a bearing is disposed between the roller supporting shaft and the supporting member to protect them against wear.
In this electroplating bath, the sink roller is located in the electrolyte, so that the sink roller and the bearing are always subjected to a corrosive environment. Various measures have conventionally been taken to counter corrosion of the sink roller, including improvement of material. However, no special consideration has been given to the protection of the bearing against corrosion. Therefore, the bearing would possibly be disabled by corrosion in an early stage of use. If the bearing mulfunctions, the electroplating apparatus will have to be stopped for the replacement of the bearing, greatly lowering its working efficiency.